The present invention relates to ducts for containing cables, such as optical cables, and to methods for mounting such ducts in an enclosure or conduit.
In the telecommunications industry it is common practice to string cable through a duct, which has previously been placed in an outer conduit. The cable may be electrical, optical or any other type. In recent years, data transmission through optical cable has vastly expanded. As a result, there has been a great increase in demand for cable to carry the digital data. Existing conduits, both above and below ground, have been utilized for new ducts and cables. The old contents of the conduit, usually electrical cable, are removed and ducts are installed, through which optical cables are subsequently placed. U.S. Pat. Nos. 5,027,864 and 4,565,351, the contents of which are hereby incorporated by reference, are examples of this.
Existing conduits have a limited amount of interior space. Further, the conduits may extend along a tortuous path characterized by multiple bends and adjacent length portions extending in non-planar directions. They are usually circular in cross section and often are buried or otherwise not readily accessible. The ducts, which are placed in the conduits, usually have relatively rigid, circular cross-sections but are flexible along their length. Consequently, multiple ducts are difficult, if not impossible, to insert within conduits in some cases.
Using circular duct in a circular conduit is an inefficient utilization of space. That is, there is a considerable amount of wasted space between the circular ducts. For example, a conduit with a 4″ internal diameter would hold only three ducts with a nominal 1¼″ internal diameter. This inefficient use of the conduit interior space or cross-sectional area corresponds with a low packing efficiency.
In further efforts to achieve cable installation efficiencies, consideration has been given to the mounting or stringing of cable within existing utility service lines such as gas or water lines. Such an installation technique would provide a low-cost cable pathway to a home or business. However, such utility service lines are typically not oversized for the volume of water or gas that they are intended to deliver and may only range in diameter from one to several inches. Accordingly, even though the cable conduit may be small in diameter, it would still occupy a significant volume and cross-sectional area of the service line and tend to interfere with the utility delivery.